LIVING AND DEAD CELLS 131 



be done is to be able to distinguish accurately between 

 a living and a dead leucocyte; it is impossible to say 

 how long a cell will live if there is no means of telling 

 when it is dead. It may appear strange, but it is a 

 fact, that it took two years to find out the difference 

 in the appearance between a living and a dead leucocyte. 

 During this two years many of the points regarding 

 the diffusion of substances into cells, vacuolation, and 

 achromasia were found out; but although many efforts 

 were made experimentally to try to perfect a method 

 of measuring the lives of leucocytes, this difficulty, that 

 one could not accurately distinguish between living and 

 dead cells, always stood in the way. When the point 

 was discovered, it may almost be said that it was by 

 accident, and even then its value as a method of 

 measuring the lives of the cells was not appreciated 

 for some time. 



It was known, of course, that leucocytes lived for 

 some hours after their removal from the circulation, for 

 they sometimes showed amceboid movements; but 

 in order to measure the lengths of their lives it was 

 necessary to be able to say at any given moment that 

 so many leucocytes in a given sample of blood were 

 alive, and that so many were dead. The cells were 

 always examined on jelly which contained stain; some- 

 times they show y ed movements and sometimes they- did 

 not; but the absence of movements was no evidence 

 that death had taken place. Many experiments were 

 made, and at last it was resolved deliberately to kill 

 some cells by a virulent poison, and to see whether the 

 cells so killed appeared in any way different from those 



